In boosted internal combustion engines, compressed air is delivered to the engine via a compressor, which may be driven by an exhaust turbine. The air is heated as it is compressed. During certain conditions, pressure may build up at the compressor outlet, leading to compressor surge. Compressor surge primarily leads to noise, vibration, and harshness (NVH), but can also cause compressor damage. A compressor bypass valve (CBV) may be used to release pressure in turbocharged engines. By doing this, the CBV prevents compressor surge and reduces wear on the turbocharger and engine. The CBV relieves the damaging effects of compressor surge loading by recirculating the air into the intake upstream of the compressor inlet, increasing the flow rate of air through the compressor and reducing the pressure ratio across the compressor.
A common issue with the CBV is that the valve may become stuck open or closed, causing performance issues. If the valve is stuck open, it will constantly bleed boost, which will effect torque delivery and drivability. If the valve is stuck closed, it is unable to recirculate the air and pressure builds up, potentially leading to a compressor surge. Thus, the CBV may be intermittently diagnosed to account for these issues.
In cases where the compressor bypass valve is stuck open, boost pressure may not build up even with the wastegate completely closed. This triggers an underboost condition. However the reason for underboost may not be immediately known (e.g., stuck wastegate, stuck bypass valve, leak in the air induction system, etc.) and the problem may be difficult to diagnose.
The inventors herein have recognized the above issues and provide an approach to at least partly address them. In one example, the issues described above may be addressed by a method for indicating degradation of a CBV coupled in a compressor bypass based on a comparison of intake aircharge temperature measured upstream of a compressor inlet and air temperature directly downstream of a compressor. In this way, a larger difference in temperature can be measured between ambient air and intake air to help diagnose the CBV.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.